[#0005ff]Doug Knox provides two fixes for this at his website. Go to http://www.dougknox.com and click on XP Fixes then on File Association Fixes. You then have two to choose from or take both - one is the .LNK fix if your shortcuts are messed up and the other is the .EXE fix for executable files that have gone wrong. Download both - they're quite safe to add to your Registry when prompted. Restart the computer afterwards and post back if they didn't do the trick.
Your biggest problem is yet to come - finding which nasty piece of malware that caused this to happen - scan with everythign you have and if you don't have MalwareBytes, download it from http://www.malwarebytes.org and use that to clean up.[/#000ff]